1. Field of the Invention
This invention pertains generally to magnetic random access memory (MRAM), and more particularly to read-disturbance free content addressable memory (CAM) using voltage controlled magneto-electric tunnel junctions (MEJs).
2. Description of Related Art
Memory devices with ever increasing densities, speeds and reliability are sought by the electronics industry. This demand applies to regular memory devices as well as to more specialized memories, such as content addressable memories (CAMs). Memories configured as CAMs are particularly well-suited in numerous applications, including search-based systems, such as cache controllers, Ethernet routing, data compression, pattern recognition, and so forth.
Presently available CAMs are typically implemented using SRAM-based data storage. However, static RAMs consume a large amount of power, and data is lost when the power is lost (i.e., volatile).
Toward mitigating these problems with SRAM CAMs, spin-transfer torque (STT) MTJs have recently been used to construct nonvolatile CAMs. Spin transfer torque (STT) techniques use spin-aligned (“polarized”) electrons to directly torque the domains. In particular, if the electrons flowing into a layer are forced to change their spin, this will develop a torque that will be transferred to the nearby layer. The use of currents for writing STT-RAM, however, still involves substantial energy dissipation, and provides a limited memory array density since each magnetic bit requires a large access transistor to drive its large write current, which also limits its scalability. By using a nonvolatile MRAM memory element, static power dissipation can be almost entirely eliminated by cutting the power supply during idle periods.
However, despite their area and energy benefits, the speed and reliability of these CAMs using STT MTJ is limited by their search noise margin, which is to say their noise margin when reads are performed during a search.
Accordingly, a need exists for a non-volatile CAM with a high search noise margin, a high density, and low power dissipation in both static and active operation. The present invention fulfills these needs and others while overcoming many shortcomings of previous CAM devices.